System of movable frets for stringed musical instrument



C. BARTH Sept. 3011969 SYSTEM OF MOVABLE FRETS FOR STRINGED MUSICALINSTRUMENT Filed May 27, 1968 A-r-romvevs United States Patent 3,469,489SYSTEM OF MOVABLE FRETS FOR STRINGED MUSICAL INSTRUMENT Carl Barth, 2486E. Skyline Drive, La Habra, Calif. 90631 Filed May 27, 1968, Ser. No.732,227

Int. Cl. G101! 3/06 U.S. Cl. 84-314 9 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF THE INVENTION Field of the invention The invention relatesto stringed instruments, and more particularly to fretted instruments inwhich the strings are pressed against the frets to control the note orchord produced when the strings are played.

Description of the prior art In a conventional fretted instrument suchas a Spanish guitar, the desired notes and chords are produced by firstdepressing a particular string or group of strings into engagement withthe associated frets of the guitar fingerboard, and thereafter striking,plucking or otherwise setting into vibration the guitar strings. Thecontact between the frets and the strings must be firm and solid toavoid vibrational interaction and objectionable buzzing noises. This inturn requires strong finger pressure on the strings, which alone is aconsiderable challenge to a beginner or student of the instrument.However, the problem of developing and maintaining adequate fingerpressure is compounded by the characteristic necessity of having tostretch several fingers between widely spaced frets in order to playcertain chords.

For example, where several strings must be pressed against selectedfrets on a conventional guitar, the fingers employed are arranged on thestrings as close to the selected frets as possible to thereby minimizethe amount of finger pressure required for solid fret contact. However,the length of the players fingers, distance between the selected frets,or need to crowd fingers into a small area often results in fingercontact on one or more strings a significant distance from the fret tobe employed. By the nature of the geometry in the fingerboard-to-stringrelationship, a depressed string engages the adjacent, unwanted fretfirst and it is then necessary to increase the finger pressure until thestring bears firmly against the desired fret.

The increase in finger pressure to achieve good contact increasesasymptotically as the point of finger contact moves farther from thedesired fret. Good contact becomes unachievable at some point, varyingwith fret position, instrument, and player. This results from theincreasing obstruction which the unwanted fret presents to fingerdepression.

The musician must therefore develop the technique of applying varyingpressures to the strings, according to the location of the point offinger contact in the zone between the desired fret and the adjacentfret; he must develop the endurance to apply the required fingerpressure for prolonged periods; and he must develop calluses on hisfingertips it withstand the otherwise painful bearing pressuresoccasioned when the point of finger contact is a significant distancefrom the selected fret.

Instances of bowed necks, a chronic problem in conventional instruments,result in increased finger pressures required for clear tones becausebowing upsets the normal fingerboardto-string geometry. Bowing is almostinvariably in the direction encouraged by string tension, i.e., toward ahollow fingerboard, raising the strings away from the fingerboard. Thishas the effect of an increased taper of the string plane relative to thefret plane. The effective increased taper results in a need for an evengreater depression of the string after contact with the unwanted fret topoint of contact with the desired fret. If the bridge should be loweredto compensate for this, it will result in inadequate clearance andbuzzing when frets in the upper register are employed.

Any discrepancy is one or more frets lying outside a fiat plane willresult in some degree of additional effort by the player. However,manufacture and/ or maintenance of an instrument in which frets can befixed in a perfect plane is beyond the current state of the art. Neckstraightening mechanisms are often incorporated, but these devices canonly work in the direction of reestablishing the optimum flat plane;they work against the neck as a unit and therefore cannot correct localout-of-plane conditions.

Stringed instruments of the prior art seem not to have been addressed tothe foregoing problems. Those which employ movable frets apparently doso to achieve some special musical effect, as in U.S. Patent No.2,489,657; or to simultaneously engage all strings with one fret, as inU.S. Patent No. 1,727,230; or to adjust the vibrational length of astring by some ancillary or added lever, button, key or the like notdirectly associated with the act of depressing the string for engagementwith a fret, as in U.S. Patent No. 2,368,256.

SUMMARY OF THE INVENTION The present invention provides a system ofmovable frets for stringed musical instruments, in which each fret ismovable toward an associated string as that string is depressed tothereby reduce the amount of finger pressure required to provide firmengagement between the string and the fret.

The present system can be incorporated in the stringed instrument at thetime of manufacture, and it can also be employed with existing stringedinstruments by replacement of the instrument fingerboard with afingerboard including the present system of movable frets. When fittedto the stringed instrument, the present system permits the musician toutilize normal playing techniques, without having to manipulateauxiliary devices during playing to achieve the desired reduction inrequired finger pressure. In the preferred embodiment there are nolevers, buttons, keys, or the like which protrude outside of theconventional dimensional envelope of the instrument.

The system provides a plurality of frets arranged across the guitar neckand constituting a fret set comparable to the conventional fret, and aplurality of these sets are spaced along the length of the guitar neckat the same locations as the conventional frets.

The upper surfaces of the frets lie in a static fret plane located belowthe plane of the strings, and are selectively urged upwardly toward anassociated string by means of an actuator. Preferably the actuator takesthe form of an elongated element positioned closely adjacent a stringand extending between a pair of longitudinally spaced frets. The uppersurface of the actuator is preferably located below the string plane andthe actuator is so located that When the musician depresses a string toeffect engagement of the string with a particular fret, the actuatorassociated with that fret is automatically depressed by the finger. Theacuator is suitably coupled to the fret upper surface so that as thestring and actuator are depressed, there is a corresponding upwardmovement of the fret upper surface, with firm engagement between thefret upper surface and the string occurring in a plane located above thestatic fret plane. Such engagement occurs with substantially the samefinger pressure, regardless of the location of the point of engagementof the actuator by the players finger. Moreover, it will be apparentthat the amount of finger pressure is reduced because the selected fretis moved upwardly sufficiently that the associated string is engaged ina plane high enough above the static fret plane that string depressionis not obstructed by the next adjacent fret. Consequently, the amount offinger pressure required to effect the desired string depression issubstantially unchanged, regardless of what the proximity may be betweenthe unwanted fret and j the point of engagement of the players fingerwith the actuator.

Summarizing the primary objects of the present invention, the systemreduces the finger pressures required to play a fretted stringedinstrument, reduces the variations in finger pressures required relativeto variance in finger positions between frets, alleviates the greaterfinger pressure requirements normally occasioned by an instrument havinga bowed neck, and permits finger placement farther away from theselected fret. The individual frets are each selectively movable toengage the associated string at a point which largely eliminates thepossibility of an adjacent, unwanted fret acting :as a barrier to properseating of the string on the selected fret.

Other objects and features of the invention will become apparent fromconsideration of the following description taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top plan view of the neckof a Spanish guitar incorporating the system of the present invention;

FIG. 2 is an enlarged top plan view of a portion of the system of FIG.1, illustrating a fret operative to engage an associated guitar string;

FIG. 3 is a side elevational view of the portion of the system that isshown in FIG. 2, the fret being illustrated in its normal position, inwhich it is out of engagement with the associated string;

FIG. 4 is'a view taken along the line 4-4 of FIG. 2, and alsoillustrating in dotted outline the operative position of the fret inengagement with the associated string;

FIG. 5 is a view taken along the line 5-5 of FIG. 4;

FIG. 6 is a view taken along the line 66 of FIG. 4; FIG. 7 is anenlarged perspective view of the actuator support bracket; and

FIG. 8 is an enlarged view of the spring for urging the actuator and thefret toward the positions illustrated in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT E Referring now to the drawings,there is illustrated a portion of a usual and conventional Spanishguitar which has been modified in accordance with the present invention.This modification consists in substitution of a fingerboard 10 in placeof the usual fingerboard. The fingerboard 10 could thus be .areplacement for the fingerboard of an existing guitar, or could beinstalled :as part of the original guitar. Moreover, although theinvention will be described in conjunction with a Spanish guitar, itwill be apparent that the invention is applicable for use in conjunctionwith .a variety of fretted instruments which are played by pressing thestrings upon frets to thereby con trol the note or chord resulting whenthe depressed string is plucked or otherwise played.

The fingerboard 10 is preferably an integral element attachable by anadhesive or other suitable means to the upper surface of the guitar neck12. The fingerboard 10 .4 includes a plurality of adjacent,elongatedgrooves or channels 14 corresponding in number with the numberof strings 16 of the guitar, aligned therewith, and located directlybeneath the strings 16.

The fingerboard 10 also includes a plurality of transversely oriented,longitudinally spaced channels extending across the longitudinalchannels 14, and which are each characterized by a base 18 and a pair ofopposed sloping or inclined abutments 20 and 22. The transverse channelsare shallower than the longitudinal channels 14 so that the bases 18 andabutments 20 and 22 of each transverse channel are discontinuous,providing a pair of side-by-side bases 18 and pairs of side-by-sideabutments 20 and 22 on the opposite sides of each channel 14.

At the intersection of each longitudinal channel 14 with one of thetransverse channels there is located an arcuate fret 24 so that, for thesix stringed Spanish guitar illustrated, there are six frets 24extending transversely acros the guitar neck 12 to form a set which isgenerally equivalent to the conventional continuous fret of the usualSpanish guitar. These sets of frets 24 are longitudinally spaced alongthe neck of the guitar, as best illustrated in FIG. 1.

With each fret 24 there is associated an elongated, longitudinallyoriented lever or actuator 26 generally aligned with the associatedstring 16 and subjacent channel 14. As will be seen the actuator 26extending between the adjacent .pair of longitudinally spaced frets 24is adapted for downward movement upon depression of the associatedstring 16, and the downward movement of the actuator 26 initiates anupward, pivotal movement of the adjacent fret 24 so that the string 16does not have to be pressed downwardly with the force formerly requiredin guitars of the prior art. That is, the guitar fingering constitutes adepression of the desired string 16 in combination with a simultaneousraising of the adjacent fret 24. The particular mechanism by which thefret 24 is raised in response to depression of the actuator 26 will bedescribed in detail later.

Each fret 24 is generally arcuate in configuration and includes aninclined, substantially fiat lower end 28 and a generally rounded upperend 30, the upper ends 30 of the frets 24 lying generally in a staticfret plane 32 located below the plane of the strings 16. As best viewedin FIGS. 2 and 4, the outer surface of each fret 24 is rounded orarcuate to form bearing surfaces at the ends of the fret for slidablemovement on the abutments 20 and 22 during partial rotation of the fret24. The portion of the fret 24 between the rounded ends projectsradially outwardly to define a central band 34 which extends more deeplyinto the associated channel 14, with the edges or shoulders of the band34 engaging the sides of the channel 14 to constrain the fret 24 againstlateral move ment.

The upper terminus of the band 34 forms a ledge 36 located adjacent thefret upper end 30, and this ledge is engaged by a spring 38 which tendsto maintain the fret in the normal position illustrated in FIG. 3.However, as will be seen, the spring 38 is biasable upwardly to permitpartial rotation of the fret to the dotted position illustrated in FIG.4.

More particularly, the bias means or fret spring 38 for each fret, asbest viewed in FIGS. 4, 5 and 8, fits within its associated channel 14and extends generally longitudinally of the channel. The spring 38includes a flat, generally horizontal platform 40 which at one longitudinal edge includes a pair of depending legs 42 which terminate inhorizontally disposed base portions 44 which rest upon the base or floorof the channel 14. The opposite longitudinal edge of the platform 40includes a pair of upwardly projecting spring sections 46 havingreversely formed ends which engage the underside of the superjacentactuator 26. The spring sections 46 also engage the confronting side ofa depending positioning portion 48 which is integral with the actuator26.

With this arrangement, whenever the actuator 26 is depressed from thefull line position to the dotted line position illustrated in FIG. 5,engagement between the underside of the actuator 26 and the springsections 46 causes the spring sections 46 to be biased downwardly. Thebias developed by such deformation tends to move the actuator upwardlyto return it to the position illustrated in full line in FIG. 5.

The engagement of the spring sections 46 with the portion 48 of theactuator 26 also tends to constrain the actuator 26 from lateralmovement toward the spring 38. As will be seen, movement of the actuator26 in the opposite lateral direction is constrained by engagementbetween the actuator 26 and a support bracket 50.

The spring 38 includes a U-shaped longitudinal extension 52 integralwith one end margin of the platform 40, the free end of the extension 52terminating in a reversely formed and backwardly projecting tab 54. Thetab 54 is the portion of the spring 38 which rests upon the ledge 36 ofthe fret 24 to bias it downwardly, as previously mentioned. The spring38 therefore performs the dual function of biasing both the actuator 26and the fret 24 to the full line position thereof illustrated in FIGS. 4and 5.

In addition to the depending portion 48, each actuator includes anintegral upward portion which is generally L-shaped in configuration,including an upright finger portion 56 for engagement by the musiciansfingers, and a horizontally oriented portion 58, as best viewed in FIGS.4 through 7. The depending portion 48 fits between a pair oflongitudinally spaced end tabs 60 integral with the opposite ends of thesupport bracket 50, and the bracket 50 together with the actuatorportion 48 fits within the associated longitudinal channel -14 next tothe spring 38. As will be seen, the bracket 50 not only locates andretains the actuator 26 in position in the channel 14, but alsocooperates with the spring 38 to define a fulcrum or axis of pivotalmovement for the actuator 26.

The bracket end tabs 60 are integral with a vertically oriented bracketportion 62 which rests against the adjacent wall of the channel 14. Thelower margin of the portion 62 also integrally includes a pair oflongitudinally spaced tongues 64 which extend downwardly toward the baseof the channel 14, transversely of the base, and then slope upwardlyinto engagement with the side of the channel 14 opposite the sideagainst which the portion 62 rests. The resilient tongues 64 terminatein edges which tend to dig into and seat in the channel Wall to maintainthe support bracket 50 in position in the channel 14. This permits thebracket 50 to be pressed into position within the channel 14 in a mannerwhich makes inadvertent removal of the bracket 50 from the channel 14improbable.

Also forming an integral part of the lower margin of the bracket portion62 is a stop or element 66 which is located between the tongues 64 andalso extends transversely. However, instead of engaging the oppositewall, the element 66 extends upwardly into engagement with a side of theactuator portion 48, and thus serves as a stop to maintain the actuator26 in the position illustrated in FIG. 5. In effect, the element 66resiliently opposes the biasing action of the spring section 46, whichtends to pivot the actuator in a clockwise direction.

As best viewed in FIG. 5, the upper margin of the bracket portion 62 isbent inwardly of the channel 14 and seats within a longitudinal groove68 provided in the side of the actuator 26. The upper margin of theportion 62 is further bent or deformed outwardly for engagement with theunderside of the horizontal portion 58 of the actuator, therebysupporting the actuator against downward movement in the area andproviding a fulcrum about which pivotal movement of the actuator canoccur.

Consequently, depression of the actuator portion 56 by the musicianpivots the actuator downwardly to the dotted position illustrated inFIG. 5, the pivotal movement taking place generally about an axisextending along the centerline of the longitudinal groove 68 in theactuator 26. Thus, the rotation takes place about the rounded surface ofthe reversely formed upper margin of the bracket 50.

Summarizing the interrelation of each set of fret 24, actuator 26,spring 38, and bracket 50', the actuator 26 is oriented and supported inposition by the bracket 50, which constrains the actuator 26 againstlongitudinal movement, transverse movement, downward and upward movementin the area of the upper margin of the bracket, and upward movementrelative to the upper extremity of the bracket 50'.

The spring 38 biases the actuator finger portion 56 to the full lineposition illustrated in FIG. 5, also biases the fret 24 downwardly forclockwise rotational movement to the full line position illustrated inFIG. 4, and constrains the actuator 26 against transverse movement.Moreover, since the lower end 28 of each fret 24 underlies itsassociated actuator 26, the spring 38 and the actuator cooperate tomaintain the fret 24 in position within its channel 14.

The finger portion 56 of the actuator 26 is so located that it isdepressed by the musicians finger when the finger depresses the adjacentstring 16. Such depression of the string 16, and rising of the fret 24occasioned by the movement of the actuator 26, results in engagementbetween the fret and the string in a plane which is located above thestatic fret plane 32. The point of engagement thus brings the stringaway from interference with the adjacent fret 24.

The musical instrument is played by pressing the strings 16 downwardlyin the usual manner, the act of pressing a finger against a particularstring 16 serving not only to depress the string but also to engage anddepress the associated actuator 26. The continued depression of thestring and the actuator 26 pivots the actuator generally about thefulcrum provided by the upper margins of the support bracket 50, theactuator moving downwardly against the bias of the spring 38.

Depression of the actuator 26 causes it to rotate the fret 24 upwardlyagainst the tab 54 of the associated spring 38. The upwardly movingupper end 30 of the fret 24 meets the downwardly moving string 16 toeffect the desired fretting. This occurs prior to the time that thestring 16 is depressed to the point of engagement with the next adjacentor unwanted fret 24.

When the player raises his finger from the string 16, the bias of thespring 38 returns the fret 24 and the actuator 26 to the positionsillustrated in full line in FIG. 4.

It is to be understood that the bias means 38 described above is merelyexemplary and that the present invention comprehends other means forurging the components to their normal positions illustrated in fulllines. Moreover, other means could be used to transmit movement of theactuator to the fret, it being important primarily that theinterconnection or coupling be sufliciently solid that objectionablebuzzing and rattling are eliminated.

I claim:

1. In a musical instrument having a tensioned string, the improvementcomprising:

a fret movable toward and away from said string; and an actuatoradjacent said fret and movable by the playing finger of the musicianupon depression by the finger of that portion of said string adjacentsaid fret, said actuator being operative upon such movement to effectmovement of said fret toward said string for engagement therewith.

2. The improvement of claim 1 and furthe including a bias means tendingto urge said fret away from said string.

3. The improvement of claim 1 and further including a bias means tendingto urge said actuator toward said string.

4. The improvement of claim 1 and including fingerboard means defining afret receptacle below said string and having a pair of abutments engagedby said fret, said fret being rotatable upon said abutments uponengagement by said actuator whereby a portion of said fret is movableupwardly toward said string.

5. The improvement of claim 1 and including at least a pair of saidfrets spaced along the length of said string, and wherein said actuatoris located below and generally aligned with said string, and extendsbetween said frets for engagement by the musicians fingers anywhere inthe intervening space between said frets.

6. The improvement of claim 1 wherein said actuator is elongated alongthe longitudinal axis of said string; and including a support bracket onedge of said actuator for pivotal movement of said actuator generallyabout said edge.

7. The improvement of claim 1 wherein said musical instrument includes aplurality of said tensioned strings, wherein said improvement includes aplurality of groups of said frets and actuators spaced along the lengthof said strings, and wherein each of said groups includes a plurality offrets and actuators arranged beneath and transversely of said strings,respectively.

8. The improvement of claim 7 wherein the structure of said improvementlies wholly beneath said strings.

9. The improvement of claim 7 wherein said musical instrument is aSpanish guitar and the structure of said improvement lies wholly withinthe dimensional envelope of said guitar.

References Cited V UNITED STATESPATENTS 577,930 3/1897 Prince .84-3181,727,230 9/1929 Cox 84314 2,368,256 1/1945 McBride 84-315 RICHARD YB.wrLKINsoN, Primary Examiner LAWRENCE R. FRANKLIN, Assistant Examinerf2;;3' UNITED STATES PATENT OFFECE CERTIFICATE OF CORRECTION Patent No.q 1 69 1489 Dated September 30, 9 9

Inventofla) QARL EARTH It 16 certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected an ehown below;

4 line 45' delete "2" and insert --'-3--. g e lee "U-sha )ed" and insert-.-U-'shape--. delete "position" and insert -pos1tions Column 5, line iHF- -C 1- wlsgngnq I 1mm 1:; eam; m.

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